The Electronic Frontier Foundation has filed a brief in support of accessory maker Datel, accusing Microsoft of misusing the Digital Millennium Copyright Act to quash competition in the Xbox 360 memory card market.

The case, brought by Microsoft last May, alleges Datel's SD-card-based memory cards violate the DMCA's provision against technologies that can circumvent digital protections, since they can be used to alter gamer profiles and manually change Xbox Live Achievements.

But in a brief filed today [PDF], the EFF argues the DMCA provision was intended to prevent piracy and copyright infringement, rather than to block competing accessory makers from selling compatible products.

"Letting Xbox owners use a third-party memory card does not put Microsoft at risk of copyright infringement," EFF intellectual property director Corynne McSherry said in a statement.

"Microsoft is misusing the law in order to sell more accessories and control customers' use of the Xbox. The DMCA is supposed to be a shield against piracy, not a weapon to smash competition and consumer choice."

The DMCA case came after a federal judge refused to throw out an earlier antitrust suit Datel brought against Microsoft when the Xbox 360 maker updated the system's firmware to be incompatible with Datel memory cards. That case has yet to be decided.

Microsoft has previously used the DMCA both successfully and unsuccessfully to try to prevent Xbox 360 owners from modding their consoles with chips that enable the systems to run pirated and homebrew games.